Particle focusing in a contactless dielectrophoretic microfluidic chip with insulating structures

The main purpose of the present study was to investigate the feasibility of applying the technique of contactless dielectrophoresis (cDEP) on an insulator-based dielectrophoretic (iDEP) microdevice with effective focusing of particles. The particles were introduced into the microchannel and pre-confined hydrodynamically by the funnel-shaped insulating structures close to the inlet. The particles were, therefore, repelled toward the center of the microchannel by the negative dielectrophoretic forces generated by the insulating structures. The microchip was fabricated by the technique of cDEP. The electric field in the main microchannel was generated by using electrodes inserted into two conductive micro-reservoirs, which were separated from the main microchannel by thin insulating barriers made of 20 µm-width of PDMS. The impedance of the PDMS barrier under different frequencies was measured by an impedance analyzer and the fitting curve to experimental data using the least-squares method were also addressed. The results revealed the capacitive behavior of the PDMS, in which the impedance decreased with the frequency. The numerical simulations indicated that an increase in the strength of the applied electric field significantly enhanced the performance of focusing. The preliminary experiments employing latex particles with 10 µm in diameter were conducted to demonstrate the feasibility of the present design. The usage of contactless DEP technique makes the insulator-based dielectrophoretic microchip mechanically robust and chemically inert. Furthermore, the voltage applied was also reduced rather than conventional iDEP microchip.